Retractor spool

Abstract

Force limitation in retractors is needed to avoid injury to an occupant from the seat belt itself particularly at high crash impact loads. The invention provides a seat belt retractor comprising a spool including force limiting means for allowing further payout of the seat belt webbing after the spool has locked, under the influence of an occupant's forward momentum in the crash condition. In one aspect the force limiting means is provided by a plurality of fins provided on the outer surface of the spool, each fin having a section which extends in a generally radial direction and a section which extends circumferentially, the circumferentially extending section of one fin overlapping the circumferentially extending section of an adjacent fin and supported by the radial extending section of that adjacent fin, so that a force tending to tighten the webbing on the spool, acts in a direction to crush the radial sections of the fins and to slide the circumferential sections over each other, thus reducing the effective outer circumference of the spool. In another aspect the force limiting means comprises an energy absorbing member connecting the spool to the spool shaft, the connection being rigid below a predetermined force, and above the predetermined force there being relative rotation of the spool with respect to the spool shaft to allow pay-out of belt webbing.

What is claimed is:  
     
       1. A seat belt retractor comprising a spool mounted on a spool shaft for rotation in the retractor, 
       a length of seat belt webbing wound on the spool for retraction or pay-out depending on the rotation direction of the spool;  
       means for locking the spool shaft against rotation when a crash condition is sensed;  
       force limiting means for allowing further pay-out of the seat belt webbing after the spool shaft has locked, under the influence of an occupant's forward momentum in the crash condition,  
       wherein the force limiting means is provided by a plurality of fins provided on the outer surface of the spool, each fin having a section which extends in a generally radial direction and a section which extends circumferentially, the circumferentially extending section of one fin overlapping the circumferentially extending section of an adjacent fin and are supported by the radial extending section of that adjacent fin, so that a force tending to tighten the webbing on the spool, acts in a direction to crush the radial sections of the fins and to slide the circumferential sections over each other, thus reducing the effective outer circumference of the spool.  
     
     
       2. A seat belt retractor according to claim  1  wherein the circumferentially extending fin parts are stepped so as to provide a predetermined stop for the sliding movement of the fins which provides for a minimum crushed spool size, and determines a maximum load limiting force at which pay out is allowed. 
     
     
       3. A seat belt retractor according to claim  1  wherein the fins are fixed in place relative to each other, in the undeformed spool, by shear elements, which shear elements determine a minimum force at which the load limiting comes into effect and provide a visual indication deployment. 
     
     
       4. A seat belt retractor according to claim  3  wherein the shear elements are formed of one of small ribs, pins and clips which fracture at a predetermined load which determines the minimum force.